The statements in this section merely provide background information related to the present disclosure and may not constitute prior art.
There is growing interest in being able to obtain weather related information through the use of airborne mobile platforms, for example through the use of jet aircraft. More specifically, there is growing interest in being able to measure temperature and humidity at altitudes from the Earth's surface, such as an ocean surface, up to the cruising altitude of the mobile platform.
Previously developed airborne systems have relied on performing atmospheric measurements through the use of the Global Positioning System (GPS) or through Iridium signals reflected from the ocean's surface. This method relies on changes in index of refraction as the temperature and humidity of the air in the column between the ocean's surface and the aircraft vary. However, this method requires that new antennas and new electronics devices be installed on an aircraft. This raises the cost of implementing (or retrofitting) such a weather measurement system on an existing aircraft. Thus, it is a highly desirable goal to be able to implement such a system using as many existing electronic components on the aircraft as possible.
Various other devices and systems for predicting atmospheric conditions have been used. Such devices and methods include the use of radiosondes (i.e. weather balloons) to measure temperature, humidity and other variables from the ground surface up to fairly high altitudes. Drop parachutes, which can be viewed as the equivalent of radiosondes, have also been deployed from aircraft while in flight. GPS occultation measurements have also been made from low orbiting satellites, such as the COSMIC constellation of six satellites.
Radiosonde measurements are effective but their use is limited to industrialized countries over land. The infrastructure to routinely launch and monitor them is lacking in many nations, and this method is not well suited to monitoring atmospheric conditions over the oceans. Thus, this method is generally not usable over a large portion of the Earth covered by the oceans.
Dropping small parachute packages from aircraft is technically effective, but is costly over time and may raise environmental issues.
GPS occultation with satellites makes effective measurements only at fairly high altitudes. The GPS signal is too weak to effectively traverse the lower atmosphere with enough quality to allow an occultation measurement. In addition, the spatial and temporal coverage of LEO satellite constellations is too sparse to allow comprehensive coverage.
GPS or Iridium occultation measurements from aircraft provide better coverage than measurements from satellites. Measurements also reach somewhat lower altitudes because the signal does not need to traverse the entire atmosphere twice. However, the cost to install additional antennas and occultation receivers is a limitation when considering this type of system.
Reflected signal occultation is technically better than standard occultation. The reflected signal, especially using Iridium satellites, reaches all the way to the surface, allowing a full profile of the atmosphere to be measured. However, as with standard occultation, this method requires adding antennas and receivers to the aircraft and therefore has a relatively significant cost.